FERTILISERS (GENERAL METHODS) ng
(b) Nitric Nitrogen, i gram of the fertiliser is treated with 2 c.c. of
water, the liquid filtered and the filtrate tested with cone, sulphuric acid
and ferrous sulphate in the usual way.
(c) Organic Nitrogen. In absence of ammonia, 0-5 gram of the fertiliser
is heated with soda lime : evolution of ammonia indicates organic nitrogen.
If ammoniacal salts are present, these must be removed by extraction with
water and then dried, the insoluble residue being tested with soda lime.
3. Phosphoric Acid.
(a) Phosphoric Acid soluble in Water. Half a gram is mixed with 4-5 c.c.
of water and left to stand, a little of the clear liquid being pipetted off subse-
quently and tested with ammonium molybdate.
(b) Soluble in Ammonium Citrate (Retrograde or reverted •phosphate). A
few grams are extracted several times with water and the residual insoluble
matter digested with about 20 c.c. of ammonium citrate solution (for its
preparation, see p. 123) ; the liquid is filtered and the filtrate tested with
(c) Insoluble. The residue insoluble in ammonium citrate is washed
several times with ammonium citrate solution boiled with 7-8 c.c. of nitric
acid and allowed to stand, a little of the clear liquid being subsequently
tested with ammonium molybdate.
(a) Soluble in Water. About 2 grams are boiled with 10 c.c. of water
and the liquid filtered.
To one portion of the filtrate an equal volume of 10% sodium thiosul-
phate solution is added and then 3-4 drops of Carnot's reagent1 and double
the volume of 95% alcohol: in presence of potash a yellow crystalline pre-
cipitate is formed.
The other portion is rendered faintly alkaline with sodium hydroxide,
filtered and acidified slightly with hydrochloric acid. Addition of i c.c. of
perchloric acid (D =1-12) and an equal volume of alcohol yields a white
precipitate in presence of potash.
(b) Insoluble in Water. Two grams are thoroughly exhausted with hot
water and the undissolved part boiled with a mixture of 5 c.c. of cone,
nitric acid and 10 c.c. of cone, hydrochloric acid, the liquid being diluted,
filtered, evaporated to dryness and the residue redissolved in water; this
solution is then tested as in the preceding case.
2. Determination of the Moisture
From 5 to 10 grams are heated at 100° to constant weight. Superphos-
phates and other products rich in gypsum are dried in a boiling water-oven
for 4 hours.
If the fertiliser has an alkaline reaction or it is feared that ammonia
may be lost during the drying, as, for instance, with stable manure, the
fertiliser (5 grams) is placed in a tared porcelain boat and this introduced
into a glass tube arranged in a suitable oven. One end of the tube is con-
1 100 grams of basic bismuth nitrate (magister of bisrrmth) are dissolved in the hot
in cone, hydrochloric acid and diluted to a litre with 92% alcohol., 20-30% as good, 15-20% as ordinary, and less than 15% as poor.